This invention relates to a composite material having reinforcement material, desirably particles of refractory ceramics, bonded into an amorphous metal matrix.
Hard, abrasive materials such as certain carbides, borides, and nitrides are widely used to cut other, softer materials such as metals. Large single pieces of these hard, abrasive materials are too brittle and too expensive for many cutting-tool applications.
A bonded-tool technology has developed over the years for using smaller pieces of such materials in cutting tools. In this approach, small particles of the hard, abrasive material are bonded at elevated temperatures into a matrix of a metal such as a nickel or cobalt alloy by liquid phase sintering. This process requires considerable exposure time of the components at highly elevated temperatures. Upon cooling, the resulting composite material has the particles of the hard, abrasive material dispersed throughout the metal matrix. The metal matrix bonds the particles together and also imparts fracture toughness and provides thermal conductivity to the article. As one example of this type of material, tungsten carbide/cobalt alloy cutting tools are widely used commercially.
The extended contact between the abrasive material and the molten metal during their extended contact at highly elevated temperatures can lead to chemical interactions between the particles and the molten metal, especially in the presence of reactive alloy additions to the matrix material. The chemical reactions may result in the formation of brittle intermetallic reaction products at the particle/matrix interface or within the matrix. After cooling, the reaction products may adversely affect the properties of the composite material. One solution to the problem is to coat the particles with a reaction-inhibiting coating, but such coatings are typically expensive to apply and often have limited effectiveness. Accordingly, the range of choices for the matrix material is sometimes severely limited to avoid the presence of reactive constituents. The matrix may consequently be relatively soft, weak, and susceptible to corrosion damage.
When a composite material of this type is used as a cutting tool, the surface regions of the metal matrix quickly wear away to expose the pieces of the hard, abrasive material. This exposed region acts as the cutting instrument, inasmuch as it is hard, abrasive, durable, and resistant to wear during the cutting operation. However, the underlying metal matrix which bonds the hard, abrasive material can wear away or crack with extended use and/or exposure to corrosive media. These problems are particularly troubling for those cases where there are reaction products in the matrix or the matrix was chosen to be relatively soft and weak in order to avoid the presence of reaction products. In these cases, the cutting tool may prematurely fail as the matrix material is removed or damaged, and the bonded abrasive material is undermined.
Accordingly, there is a need for an improved bonded composite material of reinforcement particles, particularly refractory ceramic particles, distributed in a matrix. Such an improved material would find immediate use in cutting tools, and also in other applications such as hard facings and structures having a high strength-to-weight ratio. The present invention fulfills this need, and provides related advantages.